Apparatus and method for transmitting and receiving data in wireless communication system

ABSTRACT

Methods for transmitting and receiving data of a station includes setting a direct route to a corresponding station and a relay route to a relay device, selecting one route as between the direct route and relay route, and transmitting and receiving data through the selected route. A non-transitory computer-readable storage medium may store a program including instructions to cause a computer to perform the method. The setting may be performed by a processor and the transmitting and receiving may be performed respectively by a transmitter and a receiver.

The present application is a Continuation Application of co-pending U.S.application Ser. No. 14/821,854 filed on Aug. 10, 2015, which is aContinuation Application of Ser. No. 14/329,623 (now U.S. Pat. No.9,113,407), filed on Jul. 11, 2014, which is a Continuation Applicationof U.S. application Ser. No. 12/746,514 (now U.S. Pat. No. 8,797,848),filed on Jun. 4, 2010, which is the national stage application ofPCT/KR2008/007177, filed on Dec. 4, 2008, and claims the benefit ofKorean Patent Applications No. 10-2007-0125697, filed on Dec. 5, 2007and No. 10-2008-0041976, filed on May 6, 2008, the subject matter ofwhich is herein incorporated by reference.

TECHNICAL FIELD

The present invention relates to an apparatus and method fortransmitting and receiving data in a wireless communication system, andparticularly, to an apparatus and method for transmitting and receivingdata using multiple routes.

This work was supported by the IT R&D program of MIC/IITA.[2007-S-002-01, Development of Multi-Gigabit Wireless InterfaceTechnologies]

BACKGROUND ART

In a wireless system, when a channel of a route that is in use isinterrupted by a person, obstacle, and the like, a condition of thechannel becomes extremely deteriorated, and thus a communication isoften disconnected. In this case, since the person or obstacle may notpermanently exist but moves, the communication interruption maydisappear. However, in a wireless communication system in a 60 GHz band,data is exchanged at high speed, as fast as 3 Gbps. Therefore, althoughthe time of the communication interruption is very short, seriousproblems may occur. Accordingly, a method of transmitting/receiving datathrough a multi-route using an Acknowledge (ACK) signal for each routeis suggested. The method verifies whether the route is interrupted basedon the ACK signal for each route and uses other routes. Therefore, themethod has a weak point that information about the route that is in useis required to be inserted in a Media Access Control (MAC) header inevery data frame. Also, although a load of the inserted information isnot heavy, power consumption for switching a beam every time whentransmitting a data packet to another route may be a burden for a devicethat is designed to be operational with a low power.

Accordingly, a data transmitting/receiving apparatus and method whichreduces a power consumption as much as possible, and which uses themultiple routes to smoothly exchange data without interruption eventhough there exists a person or obstacle in the wireless communication,is required.

DISCLOSURE OF INVENTION Technical Goals

An aspect of the present invention provides an apparatus and method fortransmitting/receiving data in a wireless communication system, whichcan smoothly communicate, even though the direct route is interrupted,through an alternative route using a relay device in addition to adirect route.

Another aspect of the present invention also provides an apparatus andmethod for transmitting/receiving data in a wireless communicationsystem, which can smoothly communication delay sensitive informationsuch as video streaming, even though the direct route is interrupted,through sequentially using a direct route and alternative routes betweenstations.

Technical Solutions

According to an aspect of an example embodiment, there is provided astation including a route setting unit to respectively set acommunication route to a corresponding station and a communication routeto a relay device, a route verifying unit to verify whether the setcommunication routes are available, a route selecting unit to select oneroute from among communication routes according to a result of theverification of the availability, and a data transceiver to exchangedata through the selected communication route.

According to another aspect of an example embodiment, there is provideda method for transmitting/receiving data of a station includingrespectively setting a direct route to a corresponding station and arelay route to a relay device, selecting one route from among the directroute and relay route, and transmitting/receiving data through theselected route.

According to another aspect of an example embodiment, there is provideda method of transmitting/receiving data of a relay device includingrespectively setting a communication route to a single station and acommunication route to a corresponding station that intends tocommunicate with the station, and receiving the data from the singlestation and transferring the data to the corresponding station.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram illustrating a data transceiver in a wirelesscommunication system according to an example embodiment;

FIG. 2 is a block diagram illustrating a configuration of a station ofFIG. 1;

FIG. 3 illustrates a message chart with respect to an internal operationof a relay device of FIG. 1;

FIG. 4 is a flowchart illustrating a data transmitting/receiving methodin a wireless communication system according to an example embodiment;

FIG. 5 illustrates a bitmap format of a Media Access Control (MAC)capability information element (IE);

FIGS. 6 to 9 illustrate a bitmap format of a Relay information element(IE);

FIG. 10 is a flowchart illustrating an antenna training procedurebetween the station and the relay device, according to an exampleembodiment;

FIG. 11 illustrates an explicit method that selects an alternative routeusing a relay switch message according to an example embodiment; and

FIG. 12 illustrates an implicit method that selects an alternative routeusing a time of communication interruption, according to an exampleembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Although a few example embodiments of the present invention have beenshown and described, the present invention is not limited to thedescribed example embodiments, wherein like reference numerals refer tothe like elements throughout.

Hereinafter, an apparatus and method for transmitting/receiving data ina wireless communication system according to the present invention willbe described in detail referring to attached drawings.

A basic concept of the present invention is to enable stations tosmoothly communicate, even though the direct route is interrupted,through an alternative route using a relay device in addition to adirect route.

A data transmitting/receiving method in a wireless communication systemaccording to example embodiment may be applicable to a WiMedia, and isnot limited thereto. The WiMdia, a compound word of a Wireless and aMedia, is a wireless technology that eliminates a connection cable in ahome networking, and enables super high-speed data transmission betweenelectric home appliances such as a PDA, MP3 player, digital TV, HDTV,DVD player, digital camcorder, digital set-top box, game console, andthe like.

A WiMedia Media Access Control (MAC) includes two MAC formats that are aDistributed Reservation Protocol (DRP) and Priority Contention Access(PCA). The DRP, which is a similar to a Time Division Multiple Access(TDMA), reserves data transmission time in advance and transmits thedata at the reserved time. That is, according to DRP, each deviceexchanges a beacon in a Beacon Period (BP) and establishes a beacongroup or extended beacon group, thereby enabling contention-freereservation data communication in the group. The PCA, which is similarto Enhanced Distributed Channel Access (EDCA) of IEEE 802.11e, performsdata transmission using a different backoff according to each priority.

FIG. 1 is a block diagram illustrating a data transceiver in a wirelesscommunication system according to an example embodiment and FIG. 2 is ablock diagram illustrating a configuration of a station of FIG. 1.

Referring to FIG. 1, the data transceiver in the wireless communicationsystem according to an example embodiment includes a first station 10,second station 20 and a relay device 30.

The wireless communication system according to an example embodimentuses a band at 60 GHZ or 1 THz and the first station 10 and secondstation 20 are in a Line of Sight (LOS).

The first station 10 and second station 20 may communicate using adirect route A established in the LOS. Also, each of the stations 10 and20 supports relaying.

Referring to FIG. 2, the first station 10 includes a route setting andantenna training unit 100, route verifying unit 200, available routestoring unit 300, route selecting unit 400 and data transceiver 500.

The route setting and antenna training unit 100 sets a direct route 1and relay route 2 between the second station 20 and relay device 30, andperforms antenna training. Here, the station 20 is a correspondingstation that intends to communicate with the first station 10.

The route verifying unit 200 verifies whether the direct route 1 andrelay route 2 are available, the direct route 1 and the relay route 2being established by the route setting and antenna training unit 100.The route verifying unit 200 stores an available route to the availableroute storing unit 300. Route data of the available route storing unit300 is updated according wireless environment.

The route selecting unit 400 is provided with available routes from theavailable route storing unit 300 and selects one from among theavailable routes. The route selecting unit 400 may preferably select thedirect route 1 to the second station 20 and, when the direct route isinterrupted, may select the relay route 2 to the relay device 30.However, the route selecting unit 400 is not limited thereto, and whenboth of the direct route 1 and relay route 2 are available, the routeselecting unit 400 may alternately select two routes according to anorder of use.

The data transceiver 500 transmits/receives data to/from the secondstation 20 or relay device 30 through the selected route. In thisinstance, the data transmitted to the relay device 30 is transferred tothe second station 20 again.

A super frame transmitted/received from the stations 10 and 20 iscomposed of a plurality of media access slots and includes a BeaconPeriod (BP) and Data Transfer Period (DTP). The BP is divided intobeacon slots and transferred. Here, a beacon performs adjusting of asynchronization of a network and the DTP transmits data according to theDRP and PCA.

Each of the stations 10 and 20 use a sector antenna or array antenna tosupport a forward transmission. This may be to establish the beacongroup, a basis of the DRP of the WiMedia MAC through supporting theforward transmission of the beacon, and to enable a contention-freecommunication between beacon groups. However, when each of the stations10 and 20 transmits data excluding the beacon, the transmission isperformed in a specific direction that is not a forward direction.

The relay device 30 is a device to provide an additional route withrespect to the first station 10 and second station 20. The additionalroute indicates an alternative route enabling data communication betweenthe first station 10 and second station 20 in addition to the directroute 1 that is established in the LOS of the first station 10 andsecond station 20. Specifically, the alternative route includes a firstrelay route between the first station 10 and relay device 30 and asecond relay route 3 between the second station 20 and relay device 30.Here, the alternative route and the direct route 1 are set not toconflict with each other.

When receiving the BP, two RF chains of relay device 30 perform in areception mode. The relay device 30 receives a beacon and transmits thereceived beacon to stations 10 and 20. Conversely, when receiving theDTP, if the relay device 30 does not perform a relay operation, two RFchains of the relay device 30 perform in a reception mode. However, whenthe relay operation is performed, the two RF chains of the relay device30 are respectively switched to perform in a reception mode and atransmission mode depending on transmission direction of data.

Specifically, when performing a relay operation, the relay device 30transfers data in an amplify-and-forward scheme as illustrated in FIG.3, simultaneously decodes a packet header to check which ACK policy isused, and performs switching of a mode of the RF Chains depending on thecheck result. Here, ACK policy may be one of a No-ACK, Immediate ACK,and Block ACK.

Specifically, when a field of the ACK policy of the decoded packetheader is the No-ACK, the relay device 30 maintains a tx and rx mode ofthe two RF Chains. When the ACK policy field of the decoded packetheader is the Immediate ACK, the relay device 30 switches both of thetwo RF Chains. That is, the relay device 30 switches a RF Chain in thetx mode into the rx mode and a RF Chain in the rx mode into the tx mode.In this instance, the relay device 30 performs switching aftercompleting transmission of the packet that is presently being relayed.Also, when the ACK policy field of the decoded packet header is theblock ACK, the relay device 30 switches the mode of the two RF Chainsaccording to a transmission time of an ACK included in the decodedpacket header.

A data transceiver using the relay device 30 in the wirelesscommunication system according to the present invention enables smoothdata communication between stations through the alternative route byusing the relay device 30 even when a direct route 1 is interrupted by aperson or obstacle.

FIG. 4 is a flowchart illustrating a data transmitting/receiving methodin a wireless communication system according to an example embodiment.FIG. 5 illustrates a bitmap format of an MAC capability informationelement (IE).

Referring to FIG. 4, first, a station sets an alternative route using arelay device in operation S100.

According to an aspect of the present invention, the station and acorresponding station may communicate through a direct route located ina LOS. Also, each station may use at least one relay route according toa type of the station and a type of an antenna included in the station.Accordingly, each station sets a relay support capability field to 1 touse the relay route, the relay support capability field being newlydefined in the MAC capability IE. Subsequently, the station includes theMAC capability IE, wherein the relay support capability field sets to 1,in a beacon or DTP and transmits.

Referring to FIG. 5, the bitmap format of the MAC capability IE definesa Priority Contention Access (PCA), Distributed Reservation Protocol(DRP), explicit, relay, and the like.

Here, one bit of Octet 1 represents a relay capability field and twobits of Octet 1 represent a relay support capability field. The relaycapability filed indicates whether a relay device perform a relayoperation. Also, the relay support capability field indicates whetherthe station supports data exchange using the relay route.

The relay device receives a beacon of other stations before transmittinga frame. Subsequently, when the relay device receives at least onebeacon during scanning a signal, the relay device transmits the beaconfrom an empty slot using a forward beam according to a beacontransmission procedure described in a wireless MAC. In this instance,the relay device transmits MAC capability IE after setting the relaycapability field of the MAC capability IE to 1.

Therefore, according to an aspect of the present invention, when thestation and corresponding station want to communicate using the relaydevice, the setting of the alternative route includes verifying whetherthe relay device exists and notifying that the station and correspondingstation want to communicate data using the relay device to each stationand relay device, thereby combining each station. The alternativesetting procedure is possible through that the station and correspondingstation transmit a beacon including the relay support capability filedthat is set to 1 and then the relay device that receives the beacontransmits the beacon including the relay capability filed that is set to1.

Subsequently, the station performs antenna training with the relaydevice in operation S110.

The relay device respectively performs antenna training with station andcorresponding station that want to communicate. Here, in the case ofwhen a directional antenna is equipped, the antenna training is aprocedure to adjust a direction of a beam of the directional antenna andreduce a width of the beam in order to transmit farther or increasethroughput.

Subsequently, the alternative route wherein the antenna training iscompleted is added to an available route list and managed.

Subsequently, the station checks a mode of a communication route inoperation S120.

The communication route between the station and corresponding stationaccording to an aspect of the present invention may include a singleroute mode and sequential multi-route mode. Here, the single route is amode wherein data is transmitted/received using one route from themulti-route between the stations. The sequential multi-route mode is amode wherein data is transmitted/received through sequentially using themulti-route between the stations. Here, the multi-route may include analternative route using the direct route located in the LOS between thestations and relay device.

Subsequently, when the communication route mode is the single routemode, the station transmits/receives data using one route from themulti-route in operation S130.

Specifically, the station transmits/receives data using one route amongthe direct route and alternative route. In this instance, the stationmay continuously transmit/receive data using the selected route untilthe one selected route is interrupted. Subsequently, when the directroute is available, the station may communicate through the direct routeagain.

For example, the station preferably transmits/receives data using thedirect route. In this instance, the direct route may be temporarily orpermanently interrupted by a person, obstacle, and the like. Then, thestation may transmit/receive the data using the alternative route.Subsequently, when the direct route becomes available, the station maycommunicate through the direct route again.

A route switching method of the station according to interruption of thecommunication route may include an explicit method that uses a relayswitch command and an implicit method that uses a time of theinterruption. The route switching method will be described in detailreferring to FIG. 11 and FIG. 12.

Subsequently, when the communication route mode is the sequentialmulti-mode, the station transmits/receives data using all of themulti-route in operation S140.

Specifically, the station may determine an order of the direct route andrelay route and transmit/receive data using the direct route or relayroute according to the determined order. However, when one of the tworoutes is interrupted, the station may transmit/receive data usingmerely one available route. Subsequently, when the interrupted routebecomes available, the station may communicate using the multi-routeaccording to the order.

For example, first, the station may transmit/receive data using thedirect route, and then transmit/receive data using the alternativeroute. Then, the station may communicate through alternately using thedirect route and the alternative route. However, when the direct routeis interrupted, the station communicates merely using the alternativeroute. Subsequently, when the direct route becomes available, thestation may sequentially use the direct route and alternative route tocommunicate.

When performing the communication, the direct route and alternativeroute may be managed as the available route list according toavailability. The available route list may be updated according toperiodical verification of the availability.

Hereinafter, a bitmap format of a Relay IE and a procedure of antennatraining between the station and relay device will be described indetail.

FIGS. 6 to 9 illustrate a bitmap format of a Relay IE.

Referring to FIG. 6, the Relay IE defines a Relay command type, Relaymode, and the like.

The Relay IE may request a command to perform a relay operation such asrelay set, relay complete, relay switch and be used in response to therequest. Specifically, bit information for each Relay command type is asillustrated in FIG. 7 and bit information for each Relay mode type is asillustrated in FIG. 8.

Referring to FIG. 8, the Relay mode type includes a tx mode field andlink order field.

The tx mode indicates a communication route mode of a station. Forexample, when the tx mode field is 0, it indicates a single route mode,and when the tx mode field is 1, it indicates a sequential multi-routemode.

The link order field indicates a route and an order of the route, whichis as illustrated in FIG. 9.

Referring to FIG. 9, the link order field may be defined according tothe route and the order of the route. Here, 0 indicates a direct routeand 1 indicates a first alternative route. Also, 2 indicates a secondalternative route. Here, although two alternative routes are described,the present invention is not limited thereto.

FIG. 10 is a flowchart illustrating an antenna training procedurebetween the station and corresponding station and relay device.

Referring to FIG. 10, first, the station and corresponding stationperform antenna training through a direct route in operation S200.

One station from among the station and corresponding station requeststhe antenna training of the direct route and the stations perform theantenna training. Subsequently, a device that requests the antennatraining, for example, a first station, may transmit a relay set requestcommand to a second station (corresponding station) using a Relay IE.Then, the second station may transmit a relay set response command tothe first station.

Subsequently, the stations and relay device perform antenna training inoperation S210.

When the first station receives the relay set response command from thesecond station, the first station may request the antenna training withthe relay device.

The antenna training between the stations and relay device may include afirst antenna training through a first relay route between a firststation and relay device and a second relay route through a second relayroute between the second station and relay device.

The antenna training between the stations and the relay device may beclassified into a sequential training and a parallel training accordingto a performance order of the first antenna training and the secondantenna training.

The sequential training is a method that the first antenna training andthe second training with respect to the first relay route and the secondrelay route are sequentially performed. A device that requests antennatraining of the direct route, for example, the first station, performsantenna training with the relay device and then the second station mayperform antenna training with the relay device. That is, after the firstantenna training is performed, the second antenna training is performed.Also, it is possible to perform the first antenna training after thesecond antenna training is performed.

The parallel training is a method that the first antenna training andthe second antenna training with respect to the first relay route andthe second relay route are simultaneously performed. The antennatraining between a device that requests the antenna training, forexample, the first station, and the relay device is simultaneouslyperformed together with the antenna training between the second stationand the relay device. In this instance, the relay device needs twomodems since the relay device simultaneously performs antenna trainingwith the station and corresponding station.

Subsequently, whether the antenna training between the stations and therelay device is completed is checked in operation S220.

The first station transmits a relay complete request command to thesecond station using a Relay IE. Then, the second station transmits arelay complete response command to the first station after the antennatraining with the relay device is completed. Throughtransmitting/receiving a complete command with respect to the antennatraining between stations, the antenna training procedure between thestations and relay device is completed.

Hereinafter, a communication route switching method between stationswill be described in detail.

For example, a station of the present invention may communicate throughan alternative route using a relay device when a direct route betweenstations is interrupted. In this instance, an alternative routeselecting method of the station includes an explicit method that usesrelay switch command and an implicit method that uses a time ofcommunication being interrupted without using the relay switch command.

FIG. 11 illustrates an explicit method that selects an alternative routeusing a relay switch message according to an example embodiment.

Referring to FIG. 11, the explicit method is a method that switches aroute using a relay switch command between stations. That is, when adevice that requests antenna training with a direct route, for example,a first station, transmits data and does not receive more than a certainnumber of ACKs with respect to the data from a second station, the firststation transmits a relay switch request command to the second stationthrough the alternative route. In this instance, the first station mayperform transmission in an omni-directional transmission.

When the second station does not receive data from the first stationthrough the direct route, the second station adjusts a beam to a relaydevice that is recognized as a result of the antenna training.Subsequently, after receiving the relay switch request command, thesecond station transmits the relay switch response command includingdetour time IE indicating a point in time when the alternative routewill be used to the first station. In this instance, the second stationperforms relay switching and uses the alternative route through a relaydevice from the detour time.

The first station receives the relay switch response command anddetermines a point of the time when the alternative route will be usedthrough the relay device using the detour time IE included in thecommand. When data communication through the alternative route isunavailable at the determined detour time, the first station may use thedirect route again using the relay switch command. The explicit methoduses the relay switch, and thereby can reliably select the alternativeroute and adjust the time when the alternative route will be used.

FIG. 12 illustrates an implicit method that selects an alternative routeusing a time of communication interruption, according to an exampleembodiment.

Referring to FIG. 12, an implicit method is a method that switches aroute using a time of disconnection data communication between stations.That is, when a device that request antenna training of a direct route,for example, a first station, transmits data and does not receive morethan a certain number of ACKs with respect to the data from a secondstation, the first station performs relay switching andtransmits/receive data using an alternative route through a relaydevice.

When the second station does not receive data from the first station fora certain time, while periodically receiving data, the second stationperforms relay switching and immediately transmits/receives the datausing the alternative route through the relay device.

However, when, although the first station transmits data using thealternative route through the relay device, the first station does notreceive an ACK with respect to the data from the second station, thefirst station may recheck a selection of the alternative route throughthe explicit method. Subsequently, when data communication through thealternative route is unavailable, the station uses the direct routeagain using the relay switch command in the same manner as the explicitmethod.

Here, a relay switching of the first station may be performed prior to arelay switching of the second station, and the reverse is possible.

The implicit method may switch the communication route more quicklythrough not using the relay switch command.

According to an example of the present invention, when a station is in asingle route mode and a selected communication route is interrupted, adata transceiver may switch the communication route using either theexplicit or implicit method.

However, when the station is in a sequential multi-route mode, thestation may sequentially use the multi-route and naturally use theimplicit method. In this case, the station may not use the relay switchcommand and may not need station switching and antenna setting withrespect to the transceiver of a relay device, thereby reducing time forswitching communication route. Therefore, when the station is in thesequential multi-route mode, as a time for switching decreases, delayand loss of data transmission may be effectively improved. Accordingly,the sequential multi-route mode of the station may be more effectivewhen the data is delay sensitive information such as video streaming.

According to an example of the present invention, a data transceiver inthe wireless communication system uses multi-route, and thereby cansmoothly transmit/receive data even when a route is disconnected. Also,the data transceiver in the wireless communication system uses tworoutes, and thereby can reduce power consumption of switching. However,a number of routes is not limited thereto, the number of routes may varyas required.

The data transmitting/receiving method in the wireless communicationsystem according to example embodiments may use an alternative routeusing a relay device in addition to a direct route between stations, andthereby can smoothly perform communication even when the direct route isdisconnected. Also, power consumption for switching may be maximumlyreduced through effectively using a multi-route.

The data transmitting/receiving method in the wireless communicationsystem according to example embodiments may be recorded incomputer-readable media including program instructions to implementvarious operations embodied by a computer. The media may also include,alone or in combination with the program instructions, data files, datastructures, and the like. The media and program instructions may bethose specially designed and constructed for the purposes of exampleembodiments, or they may be of the kind well-known and available tothose having skill in the computer software arts. Examples ofcomputer-readable media include magnetic media such as hard disks,floppy disks, and magnetic tape; optical media such as CD ROM disks andDVD; magneto-optical media such as floptical disks; and hardware devicesthat are specially configured to store and perform program instructions,such as read-only memory (ROM), random access memory (RAM), flashmemory, and the like. The media may also be a transmission medium suchas optical or metallic lines, wave guides, and the like, including acarrier wave transmitting signals specifying the program instructions,data structures, and the like. Examples of program instructions includeboth machine code, such as produced by a compiler, and files containinghigher level code that may be executed by the computer using aninterpreter. The described hardware devices may be configured to act asone or more software modules in order to perform the operations ofexample embodiments.

Although a few example embodiments of the present invention have beenshown and described, the present invention is not limited to thedescribed example embodiments. Instead, it would be appreciated by thoseskilled in the art that changes may be made to these example embodimentswithout departing from the principles and spirit of the invention, thescope of which is defined by the claims and their equivalents.

What is claimed is:
 1. A method for communicating data between a sourcestation and a destination station, the method comprising: transmitting,by the source station, data through a direct route to the destinationstation; and determining, at the source station, whether an Acknowledge(ACK) from the destination station is received during a firstpredetermined period, and upon detecting that no ACK is received duringthe first predetermined period, performing first relay switching at thesource station and transmitting the data to the destination station viaa relay route that uses a relay device, wherein, at the destinationstation, in response to a detection that no data from the source stationis received during a second predetermined period, second relay switchingis performed to receive the data via the relay route that uses the relaydevice, and wherein the second relay switching at the destinationstation is performed after the first relay switching at the sourcestation.
 2. The method of claim 1, further comprising: verifyingavailability of the direct route and the relay route; and switching fromthe direct route to the relay route, based on a result of the verifying.3. A non-transitory computer-readable storage medium storing a programcomprising instructions to cause a computer to perform the method ofclaim
 1. 4. A method for communicating data between a source station anda destination station, the method comprising: receiving, at thedestination station, data through a direct route from the sourcestation; and determining, at the destination station, whether the datafrom the source station is received during a second predeterminedperiod, and upon detecting that no data is received during the secondpredetermined period, performing second relay switching at thedestination station and receiving the data via the relay route that usesthe relay device, wherein, at the source station, in response to adetection that no Acknowledge (ACK) from the destination station isreceived during a first predetermined period, first relay switching isperformed to transmit the data to the destination station via a relayroute that uses a relay device, and wherein the second relay switchingat the destination station is performed after the first relay switchingat the source station.
 5. A non-transitory computer-readable storagemedium storing a program comprising instructions to cause a computer toperform the method of claim
 4. 6. A source station for communicatingdata, comprising: a transmitter configured to transmit data through adirect route to the destination station, and a processor configured todetermine whether an Acknowledge (ACK) from the destination station isreceived during a first predetermined period, and upon detecting that noACK is received during the first predetermined period, perform firstrelay switching at the source station and transmit the data to thedestination station via a relay route that uses a relay device; andwherein, at the destination station, in response to a detection that nodata from the source station is received during a second predeterminedperiod, second relay switching is performed to receive the data via therelay route that uses the relay device, and wherein the second relayswitching at the destination station is performed after the first relayswitching at the source station.
 7. The system of claim 6, wherein thesource station is configured to verify availability of the direct routeand the relay route, and switch from the direct route to the relayroute, based on a result of the verifying.
 8. A destination station forcommunicating data, comprising: a receiver configured to receive thedata through the direct route from the destination station, and aprocessor configured to determine whether the data from the sourcestation is received during a second predetermined period, and upondetecting that no data is received during the second predeterminedperiod, immediately perform second relay switching at the destinationstation and receive the data via the relay route that uses the relaydevice, wherein, at the source station, in response to a detection thatno Acknowledge (ACK) from the destination station is received during afirst predetermined period, first relay switching is performed totransmit the data to the destination station via a relay route that usesa relay device; and wherein the second relay switching at thedestination station is performed after the first relay switching at thesource station.